1. Field of the Invention
The present invention relates to a zinc oxide semiconductor, and more particularly, to a method of manufacturing a p-type zinc oxide semiconductor and a p-type zinc oxide semiconductor manufactured using the method.
2. Description of the Related Art
A zinc oxide semiconductor is a group II-VI semiconductor, and has the hexagonal wurzite structure. The zinc oxide semiconductor has the structure similar to the structure of a GaN-based material that is currently used in a light emitting device, and many researches have been performed on the zinc oxide semiconductor as a light source at home and abroad.
In particular, a zinc oxide semiconductor has an optical band gap of 3.37 eV at a normal temperature, and may be used as a light source in a near ultraviolet region, which makes it possible to allow a blue light emitting device to be used as a light source using a white light emitting diode. Further, an exciton bonding energy of the zinc oxide semiconductor at the normal temperature is larger than that of GaN at the normal temperature. Therefore, when the zinc oxide semiconductor is used in a field of a photoelectric device using an exciton, it is possible to expect a high optical gain. In addition, since having excellent conductivity and transparency, the zinc oxide semiconductor has been applied to various photoelectric devices, such as a transparent electrode, a sound acoustic wave device, and a varistor device.
However, the zinc oxide semiconductor is not evaporated stoichiometrically in an actual process for forming a thin film, and has the characteristic of an n-type type semiconductor due to the surplus of zinc or the lack of oxygen. The research on the manufacture of an n-type zinc oxide semiconductor has been developed heretofore, but the manufacture of a p-type zinc oxide semiconductor essential for a photoelectric device or a photoelectric device is not completely successful.
A photoelectric device emits light corresponding to an energy generated while a hole and an electron are necessarily combined with each other. Further, since a channel is formed of a hole in the case of a p-type thin film transistor, a good p-type thin film transistor should be manufactured in order to manufacture the above-mentioned electronic devices.
The reason why the p-type zinc oxide semiconductor thin film is difficult to be manufactured is that the solubility of group I and V elements for forming holes is very low in the zinc oxide. Further, hydrogen adulterated during the growth of the thin film forms a dopant-H(hydrogen) or O(oxygen)-H(hydrogen) complex body, and provides electrons into the thin film, so that holes are compensated. Therefore, there is a problem in that it is difficult to form holes in the thin film [C. G. Van de Walle et al, Nature 423, 626(2003)].
There have been the following methods of manufacturing a p-type zinc oxide semiconductor thin film that have been reported heretofore by various groups.
Japanese Yamamoto group [T. Yamamoto et al, Jpn. J. Appl. Phys. Part 2 38, L166(1999)] theoretically proposed that a p-type zinc oxide semiconductor can be manufactured using a method of simultaneously doping N (group V element) and Ga or Al (group III element).
Further, M. Joseph group [M. Joseph et al, Jpn. J. Appl. Phys. Part 2 38, L1205(1999)] manufactured a p-type zinc oxide semiconductor thin film having a carrier concentration of 4×1019/cm3 by using Ga (group III element) and N (group V element). However, it was reported that the reproducibility of these doping methods was very low, and these doping methods were not recognized as a stable and reliable method of manufacturing a p-type zinc oxide semiconductor.
T. Aoki group [T. Aoki et al. Appl. Phys. Lett. 76, 3257(2000)] reported a method of manufacturing a p-type zinc oxide semiconductor by evaporating Zn3P2 with an electron beam, and then performing a heat treatment with laser, as another method. However, it was reported that the measurement using a Hall effect for evaluating an electrical characteristic failed.
Y. R. Ryu group [Y. R. Ryu et al, J. Crystal Growth 216, 330(2000)] reported a method of manufacturing a p-type zinc oxide thin film doped with As (group V element), as another method. Further, a method of manufacturing a p-type zinc oxide semiconductor thin film, which dopes nitrogen known as an optimum dopant, has been reported in recent years [D. C. Look, Appl. Phys. Lett. 81, 1830(2002)]. However, it has been known that a semiconductor thin film having an electrical characteristic of a p-type semiconductor is changed into a semiconductor thin film having an electrical characteristic of an n-type semiconductor or an insulator, as time goes by, that is, the reliability of this method is low.
Furthermore, K. K. Kim group [K. K. Kim et al, Appl. Phys. Lett. 83, 63(2003)] reported a method of manufacturing a p-type zinc oxide semiconductor thin film by doping phosphorus (P2O5) and quickly performing a heat treatment under nitrogen atmosphere at a high temperature of 800° C. or more. However, oxygen cavities are generated on the surface of the p-type zinc oxide thin film due to the heat treatment that is quickly performed at a high temperature of 800° C. or more, so that surface fracture may occur.
In addition, Japanese Unexamined Patent Application Publication No. 2000-244014 discloses a technology for forming a buffer layer below a light emitting layer using metal. Japanese Unexamined Patent Application Publication No. 2002-16088 discloses a technology for activating a p-type dopant by performing annealing at a temperature of 450° C. or more. Further, Korean Patent Application Publication No. 2002-77557 discloses a technology that uses a quick heat treatment process in order to activate a p-type dopant, and Korean Patent Application Publication No. 2007-22991 discloses a technology that uses copper as a p-type dopant and performs a heat treatment thereon.
However, the technologies disclosed in the above-mentioned Patent Application Publications have limitation on manufacturing a highly-concentrated p-type zinc oxide thin film. That is, the technologies recover merely a part of defects in the thin film and have limitation on obtaining an electrical characteristic of a highly-concentrated p-type semiconductor by completely activating a dopant.